There has been a known technology (for example, see patent document 1) relating to a motor speed reduction device, which reduces the speed of driving force from an electric motor and outputs the reduced driving force. According to the known motor speed reduction device, rotational force inputted from an outer-rotor-type electric motor is reduced by means of a reduction gear mechanism having a planetary gear mechanism. According to the motor speed reduction device of the known technology, an amount of projection of the electric motor in a radial direction is reduced and the size of the electric motor in a rotation axis direction is also reduced.